Copper. Tin. Iron. So far, so good. These are all fairly safe things. What about mithril. Is it dangerous to smelt and work with it in an open setting in the middle of a major city? Or worse, an unventilated room?

Then there's thorium. That's a nuclear fuel. Can you imagine if people were commonly melting down uranium, purifying it, and then making armor with that? What happens to the slag? Do we purify it to get the more or less radioactive isotopes? What about the radium that is generated by decaying thorium? Powdered thorium can spontaneously burn in air at near-normal temperatures, though that's true of many metals. It should have no problem exploding in a forge.

Just to the next expansion and we're working with fel iron. Fel iron? As in, iron that has been corrupted by demonic energy? It's not as if we forge it into something that isn't demonic, making either fel iron bars or felsteel. That is followed by adamantium, which is likely mostly safe, and given the willingness of vendors to purchase it, seems to have some ability to be recycled. Due to its name and rarity, I'd guess that khorium is terribly radioactive or in some way unstable. Why we would then mix that with demon-tainted iron is anyone's guess.

Cobalt. Well cobalt doesn't sound so scary, right? It really isn't, except for cobalt-rich ores tending to produce arsenic when smelted. It is named from kobold (which means goblin). And for some reason, despite being commonly found as a by-product of copper production in real life, it is instead found in pure form and is never seen during copper production. Perhaps it isn't actually cobalt and we've been working with some terrifying other mineral. Or it comes from meteor impacts. But how often do we see meteors? How much more often do we see infernals crash down?

Saronite is the blood of an Old God.

Elementium and Obsidium don't sound like anything all that scary, though it is a little odd that we only discover the latter after Deathwing triggers the Cataclysm. The original elementium was also an extraordinarily rare and expensive alloy created from a variety of materials recovered from hostile elementals. The new version is much easier to find and smelt, but is entirely incompatible, suggesting that, despite having the same name, it is something different. What are we working with? Pyrite is a sulfur-iron compound, which seems dangerous to be smelting, and who knows how we're turning that into something other than poor-quality iron bars.

Ghost iron.

Kyparite, as best as I can tell, is fossilized amber. That's where you get transgender dinosaurs, a stirring soundtrack, and certain death.

Engineering is supposed to be horribly dangerous and irresponsible. But blacksmithing? No one said that it would be hammering radiation, demons, ghosts, and congealed madness into armor.